Malfunction Indicator Lamp (MIL) Inoperative
Circuit Description
The Malfunction Indicator Lamp (MIL) "Check Engine" lamp should always be illuminated and steady with the ignition "ON" and the Engine stopped. Ignition feed voltage is supplied to the MIL bulb through the meter fuse. The Powertrain Control Module ([1][2]PCM) turns the MIL "ON" by grounding the MIL driver circuit.
Diagnostic Aids
An intermittent MIL may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside the insulation. Check for the following items:
- Inspect the [1][2]PCM harness and connections for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.
- If the Engine runs OK, check for a faulty light bulb, an open in the MIL driver circuit, or an open in the instrument cluster ignition feed.
- If the Engine cranks but will not run, check for an open [1][2]PCM ignition or battery feed, or a poor PCM to Engine ground.
Test Description
Number(s) below refer to the step number(s) in the Diagnostic Test:
2. A "No MIL" condition accompanied by a no-start condition suggests a faulty [1][2]PCM ignition feed or battery feed circuit.
9. Using a test light connected to B+, probe each of the [1][2]PCM ground terminals to ensure that a good ground is present. Refer to PCM Terminal End View for terminal locations of the PCM ground circuits.
12. In this step, temporarily substitute a known good relay for the PCM relay. The horn relay is nearby, and it can be verified as "good" simply by honking the horn. Replace the horn relay after completing this step.
17. This vehicle is equipped with a [1][2]PCM which utilizes an electrically erasable programmable read only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
Diagnostic Test
1. Was the "On-Board Diagnostic (OBD) System Check" performed?
[YES] Go to Step 2.
[NO] Go to OBD System Check. Initial Inspection
2. a. Attempt to start the Engine.
b. Does the Engine start?
[YES] Go to Step 3.
[NO] Go to Step 6.
3. a. Check the meter fuse for the instrument cluster ignition feed circuit.
b. Is the fuse OK?
[YES] Go to Step 4.
[NO] Go to Step 16.
4. a. Ignition "ON", probe the ignition feed circuit at the cluster connector with a test light to ground.
b. Is the test light "ON" ?
[YES] Go to Step 5.
[NO] Go to Step 13.
5. a. Ignition "OFF".
b. Disconnect the [1][2]PCM.
c. Jump the MIL driver circuit at the [1][2]PCM connector to ground.
d. Ignition "ON".
e. Is the MIL "ON" ?
[YES] Go to Step 10.
[NO] Go to Step 11.
6. a. Check the [1][2]PCM ignition feed and battery feed fuses (15-A Engine fuse and 15-A PCM fuse).
b. Are both fuses OK?
[YES] Go to Step 7.
[NO] Go to Step 15.
7. a. Ignition "OFF".
b. Disconnect the [1][2]PCM.
c. Ignition "ON".
d. Probe the ignition feed circuit at the [1][2]PCM harness connector with a test light to ground.
e. Is the test light "ON" ?
[YES] Go to Step 8.
[NO] Go to Step 12.
8. a. Probe the battery feed circuit at the [1][2]PCM harness connector with a test light to ground.
b. Is the test light "ON" ?
[YES] Go to Step 9.
[NO] Go to Step 14.
9. a. Check for a faulty [1][2]PCM ground connection.
b. Was a problem found?
[YES] Verify repair.
[NO] Go to Step 10.
10. a. Check for damaged terminals at the [1][2]PCM.
b. Was a problem found?
[YES] Verify repair.
[NO] Go to Step 17.
11. Check for an open MIL driver circuit between the [1][2]PCM and the MIL.
b. Was a problem found?
[YES] Verify repair.
[NO] Go to Step 18.
12. a. Substitute a known "good" relay for the PCM main relay.
b. Was the malfunction fixed?
[YES] Verify repair.
[NO] Go to Step 13.
13. a. Repair the open in the ignition feed circuit.
b. Is the action complete?
[YES] Verify repair.
14. a. Locate and repair the open [1][2]PCM battery feed circuit.
b. Is the action complete?
[YES] Verify repair.
15. a. Locate and repair the short to ground in the [1][2]PCM ignition feed circuit or PCM battery feed circuit.
b. Is the action complete?
[YES] Verify repair.
16. a. Locate and repair the short to ground in the ignition feed circuit to the instrument cluster, and replace the fuse.
b. Is the action complete?
[YES] Verify repair.
17. a. Replace the [1][2]PCM.
IMPORTANT: The replacement [1][2]PCM must be programmed.
[YES] Verify repair.
18. a. Check the MIL driver circuit for a poor connection at the instrument panel connector.
b. Was a problem found?
[YES] Verify repair.
[NO] Go to Instrument Panel, Gauges, and Warning Indicators.